By default, software iSCSI and dependent hardware iSCSI initiators start one iSCSI session between each initiator port and each target port.
If your iSCSI initiator or target has more than one port, your host can establish multiple sessions. The default number of sessions for each target equals the number of ports on the iSCSI adapter times the number of target ports. You can display all current sessions to analyze and debug them. You might add sessions to the default for several reasons.
- Cloning sessions - Some iSCSI arrays support multiple sessions between the iSCSI adapter and target ports. If you clone an existing session on one of these arrays, the array presents more data paths for your adapter. Duplicate sessions do not persist across reboot. Additional sessions to the target might have performance benefits, but the result of cloning depends entirely on the array. You must log out from an iSCSI session if you want to clone a session. You can use the esxcli iscsi session add command to clone a session.
- Enabling Header and Data Digest - If you are logged in to a session and want to enable the Header and Data Digest parameters, you must set the parameter, remove the session, and add the session back for the parameter change to take effect. You must log out from an iSCSI session if you want to clone a session.
- Establishing target-specific sessions - You can establish a session to a specific target port. This can be useful if your host connects to a single-port storage system that, by default, presents only one target port to your initiator, but can redirect additional sessions to a different target port. Establishing a new session between your iSCSI initiator and another target port creates an additional path to the storage system.
Caution: Some storage systems do not support multiple sessions from the same initiator name or endpoint. Attempts to create multiple sessions to such targets can result in unpredictable behavior of your iSCSI environment.
